THE CHEMICAL ESTIMATION OF TYROSINE AND TYRAMINE

Abstract

Chemical Estimation of Tyrosine and TyramineThe interaction of l-nitroso-2-naphthol and tyrosine to yield a red compound has long been used as a test for this amino acid in biological extracts.This reaction has been used for the quantitative determination of tyrosine (l-3), but it is not satisfactory because the red derivative is unstable.Further investigation of the reaction in this laboratory has shown that the red compound derived from both tyrosine and tyramine gives rise, when heated in nitric acid solution, to a stable yellow substance which can be separated from excess nitrosonaphthol.With the use of this reaction, sensitive and reproducible methods for the assay of tyrosine and tyramine in biological material have been developed. Chemistry of ReactionUnder appropriate conditions, l-nitroso-2-naphthol reacts with tyrosine, tyramine, and many other substituted phenols to yield red-colored derivatives.These products rapidly change to stable yellow substances from which the excess reagent can be separated by extraction into ethylene dichloride or chloroform.The tyrosine and tyramine derivatives were prepared to determine some of their physical and chemical properties.Tyramine Derivative-l gm. of tyramine hydrochloride and 2 gm. of l-nitroso-2-naphthol were dissolved in 250 ml. of ethanol.To this were added 150 ml. of 2 N nitric acid.The mixture was heated at 55" for 3 hours and cooled.Excess nitrosonaphthol was removed by three extractions with 150 ml.portions of chloroform.An equal volume of water was added, whereupon crystals appeared.These were washed with water, dissolved in 90 per cent alcohol, and recrystallized by the addition of ether to yield 225 mg. of orange crystals; m.p.,236-237".The compound was readily soluble in hot water and in alcohol, relatively insoluble in ether and in chloroform.It could not be extracted from water into chloroform until bicarbonate was added, suggesting that the crystalline compound was a nitric acid salt.The absorption spectrum of the derivative is presented in Fig. 1.Elementary analysis of the salt indicated that 1